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Old 23-10-2010, 15:34   #16
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The differences in VHF and SSB/HAM radio noise is because the VHF is a FM or frequency modulation radio. It's inherently pretty immune to normal noise which is of AM or amplitude modulation. In other words, static generated by lightning, any kind of arcing, or other pulse type noise which can come from a refrigerator, depth sounder, (or you name it) is detected by the AM receiver in a HAM or SSB HF radio.

A VHF radio only responds to a signal which is changing frequency. That pretty much rules out any environmental or other RF type of noise.

Steve B.
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Old 23-10-2010, 16:44   #17
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The differences in VHF and SSB/HAM radio noise is because the VHF is a FM or frequency modulation radio.
Well, that is just not the case. While it is true that FM receivers are much more immune to atmospheric noise, the main difference here in regards to noise is frequency, not modulation. Atmospheric noise, primarily produced by lightning (which can propagate hundreds or thousands of miles) falls off rapidly with frequency, especially as you go above 30Mhz. It is pretty much negligible at 156Mhz (marine band) regardless of modulation. This is reverse of the effects of internally generated noise which becomes more significant as frequency increases.

Eric
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Old 23-10-2010, 17:47   #18
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G'day, RDW. An FYI. The older ICOM 802s have a "clipping" issue, as you are transmitting, in simple terms, it stops sending out your signal. This is a known fault with this radio and it should be repaird before you head offshore. You will need to determine if your 802 has had the needed modifications to stop the clipping. A temporary fix is to cut back on the output power setting to under 20%. Cheers.
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Old 23-10-2010, 18:08   #19
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Eric,

If that's true, how come an analog television set using an outside antenna can have ignition noise in the picture but no noise in the sound?

(Analog TV channels 2-13 went from 54 mhz to over 200mhz)

Television Frequency Table

VHF FM marine radios operate in the 156 Mhz band.

VHF Marine Radio Service Frequency Table

Answer to the question: The analog TV picture used Amplitude Modulation while the sound was Frequency Modulation at 4.5 mhz above the video carrier. Each channel had a 6 mhz bandwidth.

When I was a kid, nobody had cable, and lots of people had oil furnaces which made 60 hz dotted lines on the picture no matter what channel was on.
When we got cable, the lines went away. Therefore, the interference was being picked up by the antenna. Even on channel 13.

BTW, I used to own and operate a TV sales and repair business for over 30 years.
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Old 23-10-2010, 18:10   #20
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Well, that is just not the case. While it is true that FM receivers are much more immune to atmospheric noise, the main difference here in regards to noise is frequency, not modulation. Atmospheric noise, primarily produced by lightning (which can propagate hundreds or thousands of miles) falls off rapidly with frequency, especially as you go above 30Mhz. It is pretty much negligible at 156Mhz (marine band) regardless of modulation. This is reverse of the effects of internally generated noise which becomes more significant as frequency increases.

Eric
Just to prove Eric's point, I have on occasion, had 2 radios operating side by side on the same power source etc. One was a marine VHF (FM & 155 MHz), the other was an airband VHF (AM & 130 MHz); the noise levels were very similar unless there was heavy local thunderstorm activity, then the AM unit was a little noisier but generally there was not much difference between them.

Sorry for the thread drift but as Illusion pointed out, it is important to the fundamentals of system before troubleshooting it.
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Old 23-10-2010, 18:23   #21
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This is turning into a significant HAM munch fest
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Old 23-10-2010, 18:26   #22
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Heck, we haven't even started on the ham yet - but when we do, I am outta here
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Old 23-10-2010, 19:40   #23
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Originally Posted by senormechanico View Post
Eric,

If that's true, how come an analog television set using an outside antenna can have ignition noise in the picture but no noise in the sound?
It CAN have noise in the sound and because the noise levels your talking about are from very nearby sources and thus are relatively large even at these higher frequencies, and the bandwidth of the picture portion of the signal is VERY wide as compared to the bandwidth of the sound envelope. A nearby lightning strike can be heard as a static crash on your marine VHF as well as your old analog TV. It can also be heard on your marine HF hundreds of miles away because the noise level is much higher at those much lower frequencies.

Your missing the point. All that constant noise you hear on the HF is from the total sum of noise primarily from lightning but also from other man-made sources and comes from great distances. This average level of background atmospheric noise is so low at VHF marine and is so dominated by internal receiver noise that it is negligible. Yes, strong levels of noise from nearby sources can be heard at 156Mhz (AM and FM) but it is not the norm. I'm looking forward to getting back on the 40 and 80 meter ham bands now that summer is over and these bands are much quieter without all the lightning in the northern hemisphere over the winter. This is of no consequence whatsoever on my marine VHF. Not because it is FM, but because it is at 156Mhz. I also operate 2-meter SSB which is at 146Mhz. There can be some noise on occassion because it is AM but nothing like operating SSB at 2-30Mhz where noise levels are much much higher.

BTW, I'm an electronics service technician with over 35 years of experience.

Eric
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Old 23-10-2010, 20:00   #24
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G'day, RDW. An FYI. The older ICOM 802s have a "clipping" issue,
Since Icom will do this mod for no charge other than shipping you might just want to go ahead and get it done if need be. There is a way to inspect the main board to see the mod but just give them the serial number of your radio and they can tell you if it's been done or not. It is only a problem though on installations with less than optimal antenna/ground systems. They designed the automatic power control circuitry to be very aggressive when the swr between radio and tuner goes over about 1.8:1 So aggressive that it actually cuts off the transmitter on voice peaks which sounds like clipping on the receive end and makes it nearly impossible to understand what your saying.

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Old 23-10-2010, 20:11   #25
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RDW-
Noise can be a long hard chase. If the radio was purchased new and is still under warranty, I would suggest calling Icom America and documenting the issue with them, so that IF it proves to be a problem in the radio, the problem will be covered under warranty.

If you take the radio off the boat, run it from a battery in a "radio quiet" location (which probably means a field with your car engine turned off<G>), and you STILL have noise, then it becomes a question of asking Icom what to fiddle with on the front panel. Or, to send it in to them to make Really Damned Sure there's nothing wrong.

In terms of chasing radio noise and RFI in general, you should be able to find some hams, some ham club, in your area where someone has experience with this. Generally...you want everything turned off and the radio running on a fully charged battery. Many radios require "13.8 volts +- 10%" and can actually generate noise and work poorly by 12.42 volts--which most of us would call a "good" 12V source.

If you are testing it on a boat, wire it up directly to the battery with jumper cables, and make sure everything else is turned off. If at home, literally, pull every fuse in your box. The oddest things generate RFI these days. From the ARRL.ORG web site you can order "The ARRL RFI BookPractical Cures for Radio Frequency Interference. Order No. 9892 - $29.95" although they are available discounted from other sources.

The 802's are considered to be fine radios, which unfortunately also means "good at picking up noise". Although if it was used, it is possible someone monkeyed inside it, which can make a trip to Icom a not inexpensive but worthwhile trip before you start pulling power to everything else.

The big easy question, of course, is when you pull all the plugs, power down all the other breakers and gizmos, does the radio still find noise?
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Old 24-10-2010, 07:35   #26
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I appreciate all the comments. Unfortunately, as I said I am moderately ignorant and need to to a lot of reading.
I bought the radio new in 2008 and it was installed by someone who should have known what the were doing, i.e. major high end boat builder.
When I try various channels there is a set of bars in the bottom right of the screen with (-) being the least noise and (----) being the most noise. Again this is from my limited knowledge. I seem to always have about (---), no matter what channell.
I also have a Pactor Modem. I can receive weather faxes but they are so snowy that you can just barely maybe make out the contours of the large land masses.
I am set up to be able to send out emails and I have not been successful.
This all being said. I have not spent much time working on this issue because I have been trying to learn a lot about my boat, it is 650 miles away, and I have not been on it much of any time that I have not had guest and doing lots of other stuff.
Enough for the explaination or excuses:
My plan now is to :
Get the ARRL RFI book
My boat has so much wiring that is would seem impossible to get radio equipment away from other wiring. It has one of everything. I am thinking I should get a bag full of toroids and but them on any and every thing. Can I hurt anything by putting too many toroids on except my pocket book? Do I put toroids on the radio's wiring or the wiring of other equipment, or both?
I am going to run power directly to the radio instead of thru the circuit board, put fuses in both lines and simply turn the radio on and off at the radio.
I am going to use an AM radio tuned between channels to wave around my nav station to try to find sources of noise. Is there a better tool that would be easily availible
Again thanks to all the help. I am sure it may sink in.
RDW
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Old 24-10-2010, 08:20   #27
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I have my radio fed directly from a protected battery (so domestic bank can't drain it) via a relay capable of taking the 35 amp max current drain of the M802 on TX at full power/modulation. This allows me to have a switched low current circuit to control relay & isolate power if necessary.

I have a large ferrite on the power cable & another on the antenna tuner cable, plus a line isolator on main coax antenna feed near the tuner input. Never tested to see the effects of each but you can't have too may ferrites on cables particularly if you have a Pactor installation.

BTW not sure if mentioned already, but check your antenna tuner is working correctly. After changing to a particular frequency, press the TUNE button - you should see the displayed THRU message change to TUNE if its not displaying that already. This has a significant effect on receive as well as transmit.

Another check is to change then TUNE antenna to a station on a low band. Then switch to a weak station on a much higher band. After pressing the TUNE button you should hear a significant increase in the signal.
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Old 24-10-2010, 08:26   #28
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Hi RDW,
Yo can use an inductive amplifier to find noise. It is sometime referred to as fox and hound. [IMG]//http://lh3.googleusercontent.com/public/NajevnTmUqh8dlad6SUEQ-LNotsahKRHe_zx5wYhnluNnuc8IbYjgzUstFGl9Ln8IRtGXVmr drbVr-7PDNPbTNkbGkWFBzG51VuRcIMncu2xow89ztLeXKuwU_WjEh7p 5EY-7Ywqlp1QqT2iwGkfXezHJ13Jq_2ty_1I[/IMG]
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Old 24-10-2010, 09:17   #29
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IWhen I try various channels there is a set of bars in the bottom right of the screen with (-) being the least noise and (----) being the most noise. Again this is from my limited knowledge. I seem to always have about (---), no matter what channell.
Make sure the RF gain is set to maximum (9). The signal strength bars are only meaningful at this setting. When you turn the gain down you are increasing the AGC voltage and the receiver see's this as a signal at the input when in fact there isn't one. This is normal operation for many receivers. Turning the gain down, makes the signal strength meter go up.

Also, be advised that if you connect the M802 directly to the batteries without a switch, there will be a current drain of around 100ma even when the radio is turned off. This is due mainly to the crystal oven which keeps the main reference oscillator's crystal at even temperature for stability.

Eric
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Old 24-10-2010, 10:34   #30
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These are not causes of noise, they are just two ways that noise is propagated.




While there is internal receiver noise generated in our HF radio's, it is totally dominated by environmental (atmospheric) noise by some 30 to 70db so receiver noise never comes into play.

Eric
Isn't semantics wonderful...

As others have correctly pointed out, ambient (environmental) noise can easily be overwhelmed by internally generated hash from any number of maladies internal to the radio which is why I suggested it as a possible cause.

Now that we've all proved the point that there are too many variables, misunderstanding and guesses to diagnose this via internet...
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